Abstract
Some of upstream ORFs (uORFs) in 5′UTR are known to repress translation of downstream major ORF. In these cases, ribosome reinitiates translation at ATG of downstream ORF after translation termination of uORF. It was reported that the ribosomal protein L24 (RPL24) is involved in translational reinitiation of polycistronic mRNA. Here we report that an Arabidopsis mutant, in which an RPL24 gene was deleted, has unique phenotypes in gynoecium development. Similar gynoecium defects have been shown in ett and mp mutants. Because ETT and MP have uORFs, we examined whether their uORFs affect the translation efficiency of downstream ORF by mesophyll protoplast transient expression assay with reporter genes placed at downstream of the 5′UTR. The results showed that their uORFs repress the expression of downstream ORFs. We hypothesize that the gynoecium phenotypes shown in L24 mutant were caused by decrease of reinitiation efficiency of ETT and/or MP translation.
